Polybenzimidazole (PBI) has been widely used owing to its excellent mechanical and physical characteristics, and in particular, used for the production of fire wall or fire coat owing to its strong heat resistance.
In regard to polybenzimidazole, the structure of polybenzimidazole in which two benzimidazole compounds are directly bound each other and phenyl group not substituted with halogen is bound at No. 2 site is described in Russian (Soviet Union) patent No. 879985 and J. Org. Chem. 1977, 42(22); p 3485˜91.
The structures having substitution of halogen, hydroxy, cyano, alkoxy, or alkyl are described in U.S. Pat. No. 5,824,698, and the structure having substitution of phenyl with hydroxy is described in U.S. Pat. Nos. 5,317,078 and 5,412,059.
According to the description of U.S. Pat. No. 5,525,436, polybenzimizole thin film doped with phosphoric acid shows excellent proton conductivity at high temperature over 100° C., which directs the recent studies to the use of polybenzimidazole as an electrolyte for fuel cell at high temperature.
However, the production of polymer thin film is not easy because the isolation of polymerized polybenzimidazole from a reaction solution is very difficult owing to its low solubility in a solvent (H. -J. Kim et al., Macromol. Rapid Commun., 25, 894 (2004)).